Get some metrics about the Opal system status. The following information are returned:
`timestamp` (the EPOC time at which the metrics were collected),
`uptime` (the running time in millis),
`heapMemory` (the memory currently used),
`nonHeapMemory` (the memory that can be used),
`threads` (the current (count) and maximum (peak) numbers of threads),
`gcs` (the garbage collectors activity).